During operation of an automobile it may be desirable to bring the vehicle to a stop for a period of time, such as stopping at a traffic light, (hereafter “temporary stops”). Some vehicles may operate during temporary stops by idling an engine in an engine system. Other vehicles may stop the engine during temporary stops, even without a driver request to turn-off the engine, to reduce fuel consumption. For example, the vehicle may shutdown the engine by discontinuing fuel supply and/or ignition so that the engine spins down to rest. Then, once conditions indicate a driver's intent to launch the vehicle, the engine is automatically restarted.
One example approach for controlling engine stopping during such temporary stops is described in U.S. Pat. No. 4,515,124. Systems and devices are described for closing a throttle in an intake of an engine system as an engine's speed decreases. In this way, the throttle adjustment during shutdown may be used to reduce engine noise by reducing the cylinder air charge compressed/expanded in the cylinder.
However, the inventors herein have recognized various issues with such an approach. In particular, closed throttle operation during shutdown may degrade attempts to restart the engine in mid-shutdown operation. For example, if it is desired to restart the engine while still in the process of spinning down the engine (e.g., due to indications of, or changes in, a driver's intent to launch the vehicle), there may be insufficient air in the cylinder to generate sufficient torque via combustion to return the engine to idle speed and counteract the inertia of the engine decelerating to rest. Similarly, the engine may have already spun down to a speed range in which the engine starter, if present, is unable to properly engage the spinning engine and increase engine speed sufficiently for starting. Rather, the engine may then fully spin down and utilize a re-start from rest, which may generate a substantial delay in providing vehicle launch relative to the driver's request.